Field
The present invention relates to a hybrid electric vehicle (HEV) system, and more particularly, to a converter for an HEV system.
Discussion of the Background
FIG. 1 is a block diagram illustrating a configuration of a belt driving type 48V mild HEV system of the related art.
Referring to FIG. 1, the 48V mild HEV system for reducing an exhaust gas and enhancing fuel efficiency includes an engine 10, an integrated starter generator (ISG) 20 which is directly coupled to a crank pulley of the engine 10 by a belt 15, a 48V battery 30, a converter 40, a 48V electronic device 50, and a 12V battery 60. Although not shown, the 48V mild HEV system may include a control means, and for example, may include a hybrid control unit (HCU), a motor control unit (MCU), and a battery management system (BMS).
A main driving mode of HEVs based on such a configuration, as well known, includes an electric vehicle (EV) mode that is a pure electric vehicle mode using only motor power, an HEV mode which is an assist mode using a torque of an engine as main power and using a torque of a motor as assist power, and a regenerative braking (RB) mode where when a vehicle is driving based on braking or inertia of the vehicle, braking and inertia energy of the vehicle is generated by a motor, is collected, and is charged into a battery.
The converter 40 of the related art 48V mild HEV system, as illustrated in FIG. 1, is disposed between the 48V battery 30 and the 12V battery 60.
When a 12V electronic load increases, the converter 40 operates in a buck mode, and in the buck mode, the converter 40 converts a 48V input voltage into a 14V output voltage and supplies power to the 48V electronic device 50. When power of the 48V electronic device 50 is insufficient, the converter 40 operates in a boost mode, and in the boost mode, the converter 40 converts a 12V input voltage into a 48V output voltage and supplies power to the 48V electronic device 50.
The related art 48V converter uses phase dropping mode (PDM) technology where under a low load condition, only elements (for example, a transistor, an inductor, etc.) which operate in a necessary phase among twelve phases operate, and thus, minimize 1) a switching loss 2) an inductor conduction loss.
The 48V converter has a 12-phase (6-phase interleave, 2 parallel) structure where each of twelve phases is based on power of 200 W, and thus, supplies total power of 2.4 kW. In this case, problems of heat, noise, and/or the like are caused depending on a sequence in which elements operating in twelve phases are arranged. That is, in a PDM, due to a problem (heat concentration) where heat mainly occurs in adjacent elements which operate in four phases under a low load condition, problems such as a malfunction and/or the like are caused by a pulse width modulation (PWM) noise.